Sudden cardiac death (SCD) claims a quarter millions lives per year in the United States. Individuals with heart failure (HF) are at a higher risk for SCD. The mechanistic link between HF and SCD has not been determined. The hallmark of HF and SCD is autonomic dysfunction. Whereas ?-adrenergic (sympathetic) signaling has been extensively studied in HF, relatively little is known about the role of muscarinic (parasympathetic) signaling. Recent work by the PI has demonstrated that remodeling of muscarinic receptors is a critical component of the pathophysiology of HF. Further, cardiac resynchronization therapy (CRT), the only HF therapy to improve both acute and chronic cardiac function and survival differentially remodels muscarinic receptors to improve sympathovagal balance, ?-adrenergic responsiveness, Ca+2 handling and contraction. Therapy with vagus nerve stimulation (VNS) has salutary effects in HF patients, similar to CRT. The underlying mechanisms are largely unknown. This proposal leverages a novel guinea pig model of hypertrophic heart failure that recapitulates many features of human HF, including prolonged QT interval and a high incidence of spontaneous arrhythmic SCD. Using this unique model, the PI's novel findings and VNS, a promising new HF therapy, this proposal will test the hypothesis that time-dependent changes in mAChR expression and signaling play a critical role in the development of HF/SCD and these can be reversed by chronic VNS. The specific aims will explore new fundamental mechanistic information about how and when in the disease process mAChR remodeling may be beneficial or pathological, while testing exciting new therapies for HF/SCD. We will identify key proteins, pathways and biomarkers modified by chronic VNS using differential transcriptomics and proteomics (omics). Changes in myocyte properties are manifested in transcriptome and proteome, contributing to the HF/SCD phenotype. Echocardiography, continuous ECG and in vivo hemodynamic studies will parallel the molecular/cellular studies. In ex vivo studies, antibodies and pharmacological agents will be used to test key signaling components. The proposed program is part of the PI's long term goal to investigate molecular mechanisms of cardiac function for the development of new exciting therapies for HF and SCD.